VELOCITY OF COHERENT AND INCOHERENT ELECTROMAGNETIC-WAVES IN A DENSE STRONGLY SCATTERING MEDIUM

Frequency and time-domain experiments are conducted to present additional confirmation of the slow speed of electromagnetic waves in a dense strongly scattering medium. A wide-band microwave signal is propagated through randomly distributed glass spheres, and the speed is defined as the time at which 50% of the pulse energy arrives. Thus, the speed was measured directly without the use of the transport mean free path and the diffusion coefficient. The speed of an incoherent pulse in the Mie resonance scattering region is found to be less than 40% of the vacuum speed for a fractional volume of 11% consistent with the energy velocity. Since the incoherent wave in a dense medium is the diffuse wave, the velocity presented in this paper corresponds to the velocity of the diffuse wave and it is different from the ballistic velocity. The speed of coherent waves is found to be almost constant and is quite different from the energy velocity.